Apple Pencil Pro battery stuck at 0% after charging

Your Pencil Pro is probably dead and needs replacement. They have a very small internal battery. The device has no on-or-off switch. It's basically 'running' as soon as you take it off the side of your iPad.

I just bought a Pencil Pro that was brand new, in a sealed box. It was dead, right out of the package. Zero percent. Absolutely would not take a charge after multiple days left to charge.

Buy from a reputable reseller, who turns over their inventory and doesn't have year-old stock.

All rechargeable batteries, regardless of battery chemistry, require maintenance through periodic charging.

Be aware that if your Pencil has been set-aside for an extended period, unused and uncharged, the Pencil battery may have been damaged through deep discharge. In common with all Li-ion batteries, they must always have some level of charge. The tiny internal Li-ion battery is susceptible to permanent/irreversible damage through being left discharged for long periods. Even some “new” pencils can exhibit signs of failure out-of-the-box if they are “old stock”. 

It is essential that if you have an Apple Pencil that you charge it regularly - whether used or not - so as to protect the battery from deep-discharge. Do not allow a pencil to remain in low-charge state for any period of time - as the internal battery will fail, rendering the Pencil useless. Setting aside an unused Pencil, for extended periods, is a recipe for premature death of the Pencil battery.

For Apple Pencil Pro and the second generation Apple Pencil, both of which support inductive charging, it is recommended that the Pencil is always docked with the host iPad whenever it is not being actively used. This ensures that the Pencil is always ready for use and protected from deep discharge. The Pencil cannot be over-charged; it will only sufficient power, when needed, to maintain optimal charge.

If the Pencil Battery has failed, the only remedy is to replace the Pencil. If the battery has failed and your pencil is within its one-year warranty, you should look to having it replaced by your retailer or at an Apple Store.

Genius Bar Reservation and Apple Support Options - Apple

Gentle warming of the Pencil (such as placing on a hot water radiator), prior to attempting charging of the Pencil, can sometimes resurrect a dead Pencil battery.

If the battery is dead in the Apple pencil Pro, then how does it connect through Bluetooth? I’ve only used this pencil like twice, even though it’s several years old and paid too much for it to be useless.

When it's docked to the iPad, the charging activates the circuitry, enabling bluetooth. It pairs and everything is good until you pull it off the magnetic charger. It dies instantly and loses connection.

If you've only used the pencil twice, consider purchasing Procreate. I'm not at all an artist and I can have hours of fun just trying out the different brushes. Really. It's amazing and I think only $14? Apple would double the sales of Apple Pencils if they demo'd it with Procreate.